Studies on the Clarification of Heat Transfer Characteristic for Flow Boiling in Small Channels and its Improvement

小通道流动沸腾传热特性的澄清及改进研究

基本信息

批准号：
18360103
负责人：
OHTA Haruhiko
金额：
$ 10.24万
依托单位：
Kyushu University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2006
资助国家：
日本
起止时间：
2006 至 2007
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-18360103/
关键词：
micro channel boiling heat transfer binary mixture self-wetting

项目摘要

Flow boiling heat transfer in a single small tube is investigated by using FC72 as a test fluid. The heat transfer coefficients were measured in the ranges of heat flux 2-24kW/m^2 and mass velocity 100-400kg/m^2s. Test tube, made of stainless steel, has an inner diameter of 0.51mm and a heated length of 200mm. The tube is located horizontally in a vacuum chamber to reduce the heat loss and to minimize the time to obtain data regarded as that of steady state. In the experiments of strict inlet flow rate regulation, heat transfer characteristics were similar to those observed in normal size tubes. But if the flow rate was fluctuated up to±20% of the total under the weak inlet flow rate regulation, the trend that the heat transfer coefficient was increased with increasing vapor quality in moderate vapor quality region was disappeared and heat transfer deterioration due to partial dryout started at lower vapor quality. Boiling heat transfer characteristics in minichannels could be changed … More considerably by the existence of flow fluctuation caused by the rapid axial growth of elongated bubbles at low vapor quality. The regulation of inlet flow rate seems to be one of key parameters to reduce the scattering in heat transfer data encountered in flow boiling of minichannels.In order to enhance flow boiling heat transfer in narrow channels, the effects of liquid supply method to channels on CHF and heat transfer coefficient were investigated using atmospheric water for various combinations with gap sizes of narrow channels and volumetric flow rates. An auxiliary unheated channel for liquid supply was installed in parallel with the back side of a narrow heated channel. These channels were connected by two sintered metal porous plates. Fine V-shaped grooves were machined on the heat transfer surface of heated channel. High CHF values of 2.0×10^6 W/m^2 were measured under conditions the total flow rate is 3.60 liter/min and gap sizes are 2 mm and 5 mm. In the series of the experiments for total flow rate of 3.60 liter/min, highest heat transfer coefficients as much as 1.1×10^5 W/m^2 for gap size of 2 mm and 7.8× 10^4 W/m^2 for 5 mm were measured.The selection of working fluid for the high-performance thermal systems by applying boiling phenomena was examined. For mixtures of 1-propanol/ water, 2-propanol/ water and water/ ethylene glycol, nucleate boiling heat transfer characteristics were investigated. Alcohol aqueous solutions can be expected heat transfer enhancements due to "Marangoni effect". At low alcohol concentration region, CHF is decreased sharply by the increase in alcohol concentration. After reaching a minimum value, CHF is increased gradually up to the value of the azeotropic concentration with the increase in alcohol concentration at the region of moderate alcohol concentration. Less

以FC72为试验流体，研究了单小管内的流动沸腾传热，在热通量2～24kW/m^2、质量速度100～400kg/m^2s范围内测量了传热系数。管子由不锈钢制成，内径为 0.51mm，加热长度为 200mm。管子水平放置在真空室内，以减少热量损失并最大限度地缩短加热时间。在严格入口流量调节的实验中，得到的数据与正常尺寸管道中观察到的传热特性相似，但如果流量波动达到总流量的±20%，则结果表明。通过入口流量调节，在中等蒸汽质量区域传热系数随着蒸汽质量增加而增加的趋势消失了，并且可以改变在较低蒸汽质量下由于部分干燥而开始的传热恶化......更多很大程度上由于存在低蒸汽质量下细长气泡的快速轴向生长引起的流动波动，入口流量的调节似乎是减少微通道流动沸腾中传热数据散射的关键参数之一。为了研究窄通道内的传热，使用大气水，在狭窄通道的间隙尺寸和体积流量的不同组合下，研究了通道的供液方式对 CHF 和传热系数的影响，并安装了用于供液的辅助未加热通道。这些通道由两个烧结金属多孔板连接，在加热通道的传热表面上加工有高 CHF 值 2.0×10^6 W/。 m^2 是在总流量为 3.60 升/分钟、间隙尺寸为 2 毫米和 5 毫米的条件下测量的。在总流量为 3.60 升/分钟的系列实验中，传热系数最高。测量间隙尺寸为 2 mm 时高达 1.1×10^5 W/m^2 和 5 mm 时高达 7.8× 10^4 W/m^2。通过应用来选择高性能热系统的工作流体对于1-丙醇/水、2-丙醇/水和水/乙二醇的混合物，研究了醇水溶液的核态沸腾传热特性。在低酒精浓度区域，CHF随着酒精浓度的增加而急剧下降，在达到最低值后，随着酒精浓度的增加，CHF逐渐增加到共沸浓度的值。酒精浓度适中的区域。